Vacuum cleaners have a motor which typically drives an impeller to create a flow of air. The suction head of the vacuum cleaner has an opening in its bottom wall through which air can enter, the air carrying dirt and debris into the suction head. It is arranged that the air transports the dirt and debris by way of one or more airflow ducts within the suction head. The dirt and debris is transported through the duct(s) to a dirt-collection chamber. The air then passes through one or more filters before leaving the vacuum cleaner, the filters being arranged to trap the dirt and debris within the dirt-collection chamber for subsequent disposal.
The dirt-collection chamber can contain or comprise a disposable bag, the wall of the bag also acting as a filter. Alternatively, the dirt-collection chamber is a receptacle which can be removed from the vacuum cleaner, emptied, and re-installed into the vacuum cleaner for re-use.
Many vacuum cleaners have a rotatable brush located adjacent to the opening of the suction head. The brush is rotated and engages the surface which is being cleaned. The brush helps to dislodge dirt and debris from the surface which is then entrained in the air flow and transported to the dirt-collection chamber.
Many vacuum cleaners are mains powered, and the manufacturers of mains powered vacuum cleaners will often seek to maximise the electrical and suction power of their vacuum cleaners in an attempt to increase their marketability. Typically, the opening of the suction head is surrounded by a wall. The air is forced to pass underneath the wall and through the underlying carpet or the like whereby to dislodge dirt and debris from between the fibres of the carpet. As impellers are typically 10 to 40% efficient in use this is a relatively inefficient method of cleaning. In order to achieve higher impeller efficiencies, manufacturers have tended to develop faster spinning impellers creating higher suction. However, as it is air flow rather than suction which dislodges dirt and debris, such vacuum cleaners generally do not achieve improved dirt and debris collection efficiency. Manufacturers have therefore tended to quote electrical and suction power as an indicator of the effectiveness of their appliances rather than cleaning efficiency.
It is also known to provide battery-powered vacuum cleaners. Battery-powered vacuum cleaners employing this traditional approach cannot provide the suction power of a mains-powered vacuum cleaner without prejudicing the operating cycle of the vacuum cleaner, i.e. without unacceptably shortening the period between battery recharging, and therefore do not provide comparable cleaning performance.
Most domestic mains-powered vacuum cleaners fall into two broad classes. The first class is often referred to as cylinder vacuum cleaners. In cylinder vacuum cleaners the suction head is connected to an operating handle which in turn is connected to a flexible hose through which the dirt and debris pass on their way to the dirt-collection chamber. The dirt-collection chamber is located within a body which is separate from the suction head and which also contains the motor, the body having wheels or slides by which it may be pulled across the floor during the cleaning operation.
The second class is often referred to as upright vacuum cleaners. In upright vacuum cleaners the motor and dirt-collection chamber are carried by, or in some cases are integral with, the operating handle, so that the body containing the motor and the dirt-collection chamber typically lie above the suction head during the cleaning operation.
Battery-powered vacuum cleaners may adopt a somewhat different approach with the battery, motor, impeller and dirt-collection chamber all located in the suction head. The operating handle connected to the suction head is therefore used solely for maneuvering the suction head across the floor being cleaned.
Vacuum cleaner performance can vary considerably according to the surface being cleaned and the type of debris encountered. To collect larger debris the leading edge of the suction head should allow the debris to pass underneath and into the region of the opening. In contrast, in order to remove fine dirt and dust from floor crevices it is desirable to have all edges of the suction head seal to the surface being cleaned so that the airflow enters by way of the crevices, removing dust and debris as it flow therethrough.
Because battery-powered vacuum cleaners are more limited than mains-powered vacuum cleaners in the power of the motor they can employ, and are also limited in the capacity of the batteries they can utilise, they may employ other means to improve cleaning efficiency. A flexible cleaning strip is disclosed in GB patent 2 389 306 in relation to a battery-powered sweeper, although the cleaning strip could be adapted to a vacuum cleaner. The cleaning strip is located behind the opening in the suction head and can adopt a lowered position during forwards movement of the suction head, and a raised position during backwards movement of the suction head. During forwards movement the cleaning strip lies against the surface being cleaned and prevents fine dust passing underneath the trailing edge and being left behind. During backwards movement the cleaning strip is lifted away from the surface allowing fine dust and dirt to pass under the strip and into the region of the opening.
The suction head of the cylinder vacuum cleaner of U.S. Pat. No. 5,101,534 employs a flexible strip adjacent to the front of the suction head, the strip being deformed by the airflow to vary the gap between the front end of the suction head and the surface being cleaned.
The suction head of WO 97/15224 has two cleaning strips, one in front and one behind the opening in the suction head. A rocker mechanism is provided so that when the suction head is moving forwards the front cleaning strip is raised, whereas when the suction head is moving backwards the rear cleaning strip is raised. In each case a raised cleaning strip allows dirt and debris to pass under the cleaning strip into the region of the opening.
U.S. Pat. No. 5,101,534 also shows a bumper in the form of a resilient strip which surrounds the suction head and reduces the likelihood of impact damage to the suction head and to other articles. In common with many vacuum cleaner suction heads, at the front end of the suction head the bumper lies above a recess which communicates with the suction opening. The recess allows the suction head to pass over relatively large pieces of dirt and debris so that those pieces pass into the region of the opening where they can be lifted (by the rotating brush and/or the airflow) into the suction head.